1. Field of the Invention
The present invention relates to catalysts and processes for treating heavy feedstocks such as petroleum residuum. The invention more particularly relates to catalysts suitable for promoting hydrocracking reactions which convert such feedstocks to products having relatively lower boiling temperatures, to processes for making and using the catalysts, and to processes for using such catalysts.
2. Description of the Prior Art
Maximizing the yield of highly-valued products from crude oil often results in the production of relatively heavy hydrocarbon streams which are difficult to upgrade to lighter products. Typically, these streams are distillation bottoms resulting from the atmospheric or vacuum distillation of a crude oil or a crude oil-derived feedstream. These bottoms fractions are known as petroleum residuum or "resid." Resids typically contain only a relatively small amount of material boiling below about 1000.degree. F. at atmospheric pressure, up to several tens of percent of Ramsbottom carbon, and up to several hundred parts per million of metals such as nickel and vanadium.
Modern refinery economics demand that resids be processed to yield lighter and more valuable hydrocarbons. Typically, resid will be upgraded in a multi-reactor, supported catalyst system such as those described in U.S. Pat. No. 4,940,529 issued to Beaton et al; U.S. Pat. No. 5,013,427 issued to Mosby et al.; U.S. Pat. No. 5,124,025 issued to Kolstad et al.; U.S. Pat. No. 5,124,026 issued to Taylor et al.; and U.S. Pat. No. 5,124,027 issued to Beaton et al., all assigned to the assignee of the present invention, the disclosures of which are hereby incorporated by reference. While supported catalyst systems such as those disclosed in the foregoing patents have proven highly effective in upgrading heavy feedstreams such as resids, refiners continue to investigate other processes for obtaining valuable products from resids.
Another approach for upgrading resid is to hydrocrack resid in the presence of a soluble catalyst which is eventually precipitated to produce a solid catalyst dispersed as, for example, a suspended bed or an ebullating bed. This approach is described, among other places, in U.S. Pat. No. 4,134,825 issued to Bearden, Jr. et al.; U.S. Pat. No. 5,055,174 issued to Howell et al.; U.S. Pat. No. 5,446,002 issued to Kukes et al.; and U.S. Pat. No. 5,489,375 issued to Joseph et al., which are hereby incorporated by reference. Although the soluble catalyst is at least initially soluble in a feedstock or a carrier liquid, the soluble catalyst is generally precipitated to provide a dispersion of fine solids, such as metal disulfide particles, in the reactor.
Other researchers have reported that the presence of additional particulate matter tends to suppress coke production within a resid hydrocracking reaction zone that includes a fine catalytic dispersion of the type which may be precipitated from a soluble catalyst. U.S. Pat. No. 4,178,227 issued to Metrailer et al.; U.S. Pat. No. 4,376,037 issued to Dahlberg et al.; U.S. Pat. Nos. 4,770,764 and 4,863,887 issued to Ohtake et al.; and U.S. Pat. No. 5,320,741 issued to Johnson et al., which are hereby incorporated by reference, describe catalyst systems which contain fine contact particles and a dispersed precipitate from a soluble catalyst.
An improved process for increasing the catalytic conversion of heavy feedstocks is described in U.S. Pat. No. 4,695,369 issued to Garg et al. In the process, heavy oil and gaseous hydrogen in the presence of two metal catalysts are reportedly passed to a reaction zone. One of the metal catalysts is described as a highly effective oil soluble hydrogenation catalyst, such as cobalt, nickel, molybdenum or tungsten. The other of the metals catalysts is described as relatively inexpensive and readily available, such as zinc, iron or copper, and either oil soluble or a fine particulate. The '369 patent states that the use of a combination of a good hydrogenation catalyst and a greater amount of the relatively less expensive catalyst is found to increase the overall conversion and to decrease coke formation.
European patent application number 87307863.8 listing Eaton as inventor describes the use of overbase complexes of metal oxides and carbonates associated with metal salts as antifoulants for oil, gas and petrochemical refinery processes. The antifoulant composition is described as comprising at least one overbase complex of an oxide of a metal selected from the group consisting of Mg, Ca, Ba, Sr and Mn and mixtures thereof, and a metal salt of at least one organic complexing agent. The European application lists the crude unit, the fluid catalytic cracker and the hydrocracker as examples of oil refinery units which require the addition of antifoulant chemicals. The antifoulant composition reportedly undergoes a decomposition upon heating to afford minute particles of metal oxide or metal carbonate having a size no greater than about two microns which are used in an amount of about 5 ppm to about 1000 ppm by weight to inhibit fouling in a fouling area.
U.S. Pat. No. 5,283,217 issued to Ikura et al. describes a micro-emulsion prepared by forming an aqueous solution of a salt of a transition metal and a surfactant, adding the solution to a petroleum pitch or distillate, and mixing vigorously. Upon exposure to severe reducing conditions, the emulsion reportedly forms particles of a hydrogenation catalyst which have an average size of less than about 500 angstroms. The '217 patent states that the emulsion can be admixed with finely powdered clay, alumina, or amorphous or crystalline aluminosilicate so that when precipitation/reduction occurs colloidal clusters of metals deposit upon much larger particles of solid material.
In order to facilitate the cost-efficient upgrading of hydrocarbon feedstocks such as resid, new catalysts and processes are still required which minimize catalyst preparation costs and maximize the effectiveness of soluble catalysts under the aggressive operating conditions typically required to produce substantial quantities of lighter, more valuable products from a heavy hydrocarbon feedstock such as resid. Preferably, the new catalysts are injected as fluids so as to avoid solids handling at the processing facility.